1. Field of the Invention
The invention relates to plasma panel display devices wherein a Nobel or other plasma forming gas is located between sets of X and Y drive electrodes. Alphanumerics and vectors are written for display by energizing selected ones of the electrodes with a writing voltage. To maintain the display once patterns have been written, a sustaining voltage is applied to all electrodes in sequence, as such panels have inherent memory capability, an erasing voltage must be applied to extinguish patterns no longer wanted. A complete description of the operations of such panels is contained in U. S. Pat. No. 3,754,230 issued Aug. 21, 1973 to Ernest P. Auger and assigned to the present assignee, the specification thereof being incorporated herein by reference. Such panels are employed in a variety of applications requiring a flat display device.
2. Description of the Prior Art
Numerous types of plasma panel display devices have been constructed with a variety of methods for enclosing a plasma forming gas between sets of X and Y drive electrodes. In the most popular type of prior art plasma display panel, parallel plates of glass with wire electrodes on the surfaces thereof were spaced uniformly apart and sealed together at the outer edges with the plasma forming gas filling the cavity thereby formed. In some such panels, the metal electrodes were coated with a thin layer of glass. To maintain uniform brightness over the surface of the panel and to provide a panel with writing and substaining voltages constant throughout the panel within predetermined limits extremely fine tolerances on the spacing between plates had to be maintained. If the metal electrodes were not coated with glass the plasma forming gas would slowly react with metal eventually rendering the panel inoperative. If the metal electrodes were coated with glass to prevent reaction between the gas and the metal, high voltages had to be used to overcome the separation between electrode and gas provided by the glass. These problems as well as others combined to make fabrication of such panels time consuming, difficult to produce with automatic processes, and consequently expensive. Moreover problems in maintaining tolerances between the parallel plates limited the size of the display panels to fairly small sizes, typically no more then 12 X 12. None of these panels have the inherent capability for producing displays with a plurality of colors and none have been successfully made mechanically flexible.
Later attempts at constructing practical plasma display devices included those in which the plasma forming gas was contained in small cells or chambers in an insulating layer sandwiched between the two parellel plates containing the electrodes. Many different geometrical configurations were attempted including cylindrical and rectangular chambers. Some of these also contained the glass in long thin capillary tubes sealed between the parallel plates. All of these devices suffered from the inherent problem of misalignment between electrodes and gas chambers. In many of these, the problem of maintaining tight tolerances between the outer parallel plates still remained as the tolerance had to be imposed upon the insulating layer containing the chambers or cells for the gas. Slight differences in spacing between intersecting electrodes causes a corresponding change in the writing and sustaining voltages for the cell formed at the intersection of the electrodes. If extremely tight tolerances between parallel plates containing the electrodes is not maintained, the sustaining voltage required for cells in one portion of the panel may exceed the writing voltage for cells in other portions of the panel. Driving circuitry which produces only a single level of writing voltage and a signal level of sustaining voltage as specified for cells in the first portion of the panel would light all the cells in the second portion of the panel during normal sustain operations. Such panels are useless for all practical applications.